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Why LED streetlights are the ideal choice for spring weather conditions

roadway lighting in fog

Morning fog and afternoon showers are common during spring months. Navigating roadways during these low-visibility conditions can be difficult for drivers and pedestrians, but modern LED roadway lighting technology is making spring commutes safer for motorists.  

Driving in spring weather conditions

Rain reduces visibility for drivers and is especially debilitating at night. It directly affects perception and produces visibility changes when it comes in contact with headlamps, windshields, the road and road markings. We normally see an object when light from a source like the sun, streetlamps or our headlights reflects from the object back to the eye; rain interferes with this process in several ways.

  • Rain makes headlamps and other light sources less effective by filtering away some of their light output and reducing illumination on the road ahead.
  • When light strikes the raindrops, only a portion of the light passes through, while the rest scatters. The rain therefore blocks some of the light reflected by objects, and less light reaches the driver's eyes.
  • Poor visibility causes people to concentrate their attention directly ahead in order to see where they are going. This decreases their ability to see across their peripheral field.

Rain also affects visibility by changing the amount of light reflected from the road back to the driver's eye. Rain makes road delineations such as crosswalks less visible. The paint used in road markings includes a reflectorized material. In dry conditions, headlight illumination bounces off the reflective paint back to drivers’ eyes. However, water acts like a lens that disperses the light, meaning much of it is reflected in different directions. As a result, the lines become almost invisible to the driver.

Fog is also frequent in the spring in many parts of the world. It produces numerous roadway accidents, because a driver’s visibility is stunted to the depth of the fog. Foggy conditions can also increase accidents due to their effect on drivers’ perceptual judgment of speed and distance. We see objects based not on their absolute brightness or darkness, but on the difference between the object brightness and background. Fog lowers contrast substantially, causing objects to become fainter and less distinct. This makes it harder to navigate the roads in foggy conditions.

Increasing roadway safety with LED lighting

Modern lighting technology is increasing driver and pedestrian safety on the road during spring showers and residual fog.

The advantage of LEDs in fog and rain can be attributed to three things:

  • The inherent directionality of the beam of light emitted
  • The wavelength characteristics of white LED light
  • The frequency of that wavelength in comparison to other light sources

The difference between LED lighting and all other light sources is the predominant wavelength at which it emits energy, and how water droplets interact or affect a beam of light at that wavelength, especially as the size of those water droplets changes.

Light sources that primarily emit light energy within the blue wavelength of the visible spectrum, like LEDs, perform much better in low-visibility conditions than other light sources.

Light in the violet region of the spectral range has a shorter wavelength than light in the red region. Water vapor particles in the atmosphere will generally pass light that is in the yellow-orange-red range, but they tend to scatter blue light. This is likely due to the fact that water particles are generally of similar size to the blue wavelength. This phenomenon is called Rayleigh scattering. It’s why the sky appears blue and the sun appears yellow – the colors of visible light that makes it to the ground.

In low-visibility conditions, the size of the water particles is increased to the point where they are no longer of similar size to the blue light wavelengths. At this point, they are comparable in size to the yellow-orange-red wavelengths. The water particles tend to scatter and extinguish light in these bands but will pass blue light. This is why sunlight sometimes appears bluish or greenish through fog.

From water particle size to wavelengths, LEDs are the optimal choice for low-visibility conditions. Color temperature and lighting design are fundamental to creating the best conditions for roadways during rain and fog. By boosting visibility, LEDs keep roadways safer during showers and foggy conditions.

The Lighting reSource